The influence of mechanical and physiological methods on the breaking of dormancy of European ash (Fraxinus excelsior) seeds and the growth of saplings under in vivo conditions

Malgorzata Osmenda, Dariusz Latowski & Katarzyna Nawrot-Chorabik

with 8 figures and 3 tables

Key words: European ash, Fraxinus excelsior, origin, seedlings in vivo, saplings in vivo, dormancy, germination.

Summary
Osmenda M., Latowski D. & Nawrot-Chorabik K. 2026. The influence of mechanical and physiological methods on the breaking of dormancy of European ash (Fraxinus excelsior) seeds and the growth of saplings under in vivo conditions. – Phyton (Horn, Austria) 64–65: 123–138, with 8 figures and 3 tables.

European ash (Fraxinus excelsior) is sensitive to rapid fluctuations in ambient temperature and to drops in groundwater levels, two well-documented effects of global warming and the resulting climate change. Physiological disorders caused by heat stress and drought can already lead to a reduction of the number of viable seeds and saplings produced by the plant. Ash seeds, seedlings and saplings are also susceptible to pathogenic fungi causing root rot, rapid decline and death. For all those reasons, research was carried out on the germination rate of European ash seeds and on the subsequent development of seedlings and saplings. – Mature and immature (green) seeds were collected from different populations located in southern Poland, in the administrative areas of the Olkusz, Kan´czuga and Siewierz Forest Districts. One set of seed samples was subjected to dormancy-breaking treatments, including scarification, stratification, and application of distilled water (control) or of aqueous solutions of two different plant growth regulators, gibberellic acid (GA3) or 1-naphthaleneacetic acid (NAA); then the seeds were sown into the soil substrate. The other set of seed samples was sown directly into the soil substrate, without prior treatments intended to accelerate germination. Additional protection was provided for all above-mentioned batches by spraying the sown seeds and young seedlings with a fungicide. Batches of mature and immature seeds sown directly into the soil without fungicide spraying served as negative control. The young plants were grown singly in sowing trays on garden shelves with a shading net and an adequate runoff for surplus water from the soil substrate. – Results: (•) The largest number of viable saplings were obtained from mature and immature seeds from the Olkusz Forest District when both types of seeds were sown directly into the soil and sprayed with fungicide, without any prior treatment that would break seed dormancy. (•) Immature seed samples of all tested origins had a lower germination rate compared to the mature seed samples. (•) Mature seeds (from the Olkusz and Kan´czuga areas) treated with stratification and scarification plus aqueous GA3 solution showed a significantly higher germination rate and yielded more viable saplings than seeds subjected to the same mechanical treatments plus aqueous NAA solution. (•) The saplings obtained from the negative control batches (seeds not protected by fungicide and sown directly into the soil) died due to root rot caused by fungal pathogens, making further cultivation impossible. – Any efforts to regenerate dying populations of European ash in the forest environment are depending on the availability of viable seed material providing healthy seedlings and saplings. The origin of the seeds from different ash populations/individuals plays an important role for the quality and quantity of planting material. In practice, the obtained results will encourage observations and research of foresters regarding the identification and selection of trees producing viable seeds and offspring.